Wormwood refers to several plant species in the genus Artemisia (family Compositae), especially A. absinthium, a small, shrubby bush 50-100 cm (2-4 feet) tall with greenish-gray leaves and a pungent, acrid smell. Wormwood has been used medicinally and as a pesticide for thousands of years, while its use as a key ingredient in absinthe has ensured it a place in modern lore. Despite its infamy, debate continues about whether wormwood or the thujone it contains cause distinct mind-altering effects.

Is Wormwood Psychoactive?

In recent years wormwood has been described as psychoactive when smoked16,21,34 or brewed as a tea,21 and Erowid has published dozens of reports of such experiences.35 It has been reported to cause mild changes in attention, mood, and visual perception lasting from thirty minutes to a few hours. A feeling of warmth in the body and a distracted, spaced-out feeling that is sometimes compared to the effects of cannabis are commonly reported in Erowid experience reports. One author who smoked a homemade wormwood resin writes, "The world around [me] became crystal clear. Clear and real in a very surreal way [...]. Everything appeared clean, and perfect, and I began to feel as if I were inside a doll house."35

"While β-thujone usually occurs in greater concentrations in A. absinthium, the higher-potency α-thujone is regarded as the primary psychoactive agent."

A person who drank wormwood tea reports, "My peripheral vision seems more like normal vision, like where I'm not looking, I am looking. I can feel a fuzzy warm feeling around my body, not inside, but around me, like a hazy glow has formed. My vision also has a fuzziness to it, but I can see quite clearly."35 Despite evidence that wormwood is psychoactive, its use outside of absinthe liquors does not generally appear to inspire much enthusiasm.

Wormwood preparations--particularly oils and resins of unknown quality and concentration--can be dangerous. Weisbord et al. describe a 31-year-old male who drank approximately 10 ml of wormwood essential oil ordered over the Internet, having apparently confused it for absinthe. The patient suffered a near-fatal case of acute renal failure.36 Erowid has published a similar report of a person who ingested wormwood oil, underwent convulsions, and was hospitalized.35

The psychoactivity of wormwood is thought to be caused by two terpenoid ketones, α-thujone and β-thujone,4,37 and although these are commonly referred to in aggregate as "thujone", they differ in potency and toxicity. Thujone occurs in plants from several genera and is named for the plant species Thuja occidentalis, from which it was first isolated.16 Thujone concentrations in essential oils vary significantly between species, strains, and individual plants.

In 2007, Lachenmeier and Nathan-Maister reviewed 29 analyses of the essential oils of A. absinthium and A. pontica leaves and flowers, the two species most commonly used in absinthe. They found wide variations in both oil content and thujone concentrations.4 In A. absinthium they found an average of 0.6% essential oil (±0.3%), which contained a mean of 5.8% α-thujone (±11.4%) and 12.5% β-thujone (±15.2%), corresponding to a total combined α- and β-thujone content of about 1 mg per gram of dried A. absinthium. In A. pontica they found a mean essential oil content of 0.3% (±0.1%), and the essential oil was composed of a mean of 15.4% α-thujone (±12.0%) and 1.5% β-thujone (±12.7%), corresponding to a total combined thujone content of around 0.5 mg per dried gram. Some specimens of A. absinthium contained up to 2.5 mg of thujone per gram, while some harvested in France, Spain, and Egypt contained none.4 Other research has shown substantially higher thujone levels, up to 4.8 mg of thujone per dried gram of A. absinthium.13 While β-thujone usually occurs in greater concentrations in A. absinthium, the higher-potency α-thujone is regarded as the primary psychoactive agent.14

Thujone's Biological Mechanisms

The mechanisms behind thujone's psychoactivity are not well understood. In 1975, del Castillo et al. observed that thujone shows structural similarities to tetrahydrocannabinol (THC) and speculated that it might act on cannabinoid receptors in the brain.38 In 1993, Ott pointed out that thujone lacks the hydrocarbon-side chain of THC that binds to the cannabinoid receptor. A few years later, Meschler et al. experimentally confirmed that thujone displays only a low affinity for cannabinoid receptors, effectively putting the cannabinoid theory of thujone's action to rest.39

In 2004, Deiml et al., using human cells in vitro, demonstrated that α-thujone indirectly reduces serotonin 5-HT3 receptor activity, but whether or not this is a primary mechanism of α-thujone's psychoactive effects remains unclear.40

At high enough doses, α-thujone is known to exert convulsant effects by modulating GABAA receptor activity, functioning as a non-competitive antagonist.41 Interestingly, ethanol appears to counteract the GABA-modulatory action of α-thujone by enhancing neuronal GABAA receptor functions.41 In 2000, Höld et al. found that injecting mice with ethanol blocked the toxic effects of a fatal dose of α-thujone, as did administration of diazepam and phenobarbital--substances which, like ethanol, are GABA agonists. The alcohol in absinthe may therefore partially protect against the toxic effects of wormwood.

The inhibition of GABAA receptors by α-thujone may contribute to wormwood's psychoactive effects, particularly when co-administered with alcohol, as in absinthe. Höld et al. note that while thujone inhibits GABAA receptor function, alcohol enhances it. High levels of thujone in absinthe (around 260 mg/L) would create "a detectable to major inhibitory effect beyond that of the ethanol content". In 2004, Dettling et al. also found evidence that thujone temporarily counteracts the anxiety-reducing effects of alcohol in humans (see below).14 The authors speculated that this may be due to α-thujone's GABA action, as GABAA antagonism has been shown to increase stimulation and fear. This provides more evidence that thujone, alcohol, and GABA in the brain may produce a unique pharmacological interaction, and that absinthe's effects are distinct from alcohol intoxication alone.

Is Wormwood a Psychedelic?

Wormwood and absinthe are sometimes described as "hallucinogenic", but there is little evidence that they are psychedelics in any reasonable sense of the word. Recent reports of smoking or drinking wormwood infusions sometimes describe a vivid or dreamlike quality to perception such as the "doll house effect" described above, but rarely frank hallucinations or the kinds of visual distortions associated with psychedelics.

The idea that wormwood is hallucinogenic may be based in part on accounts of absinthism. Hallucination was a commonly described symptom of absinthism in medical journals, 5 though it would likely be described as delirium today. In 1912,the French physician Valentin Magnan, an influential proponent of absinthism as a distinct condition, wrote: "[Alcoholic delirium] is characterized by hallucination almost always of a distressing kind [...] Is the patient given to absinthe? Then the symptomatology is different. In Absinthism the hallucination insanity is more active, more terrifying, sometimes provoking most dangerous reactions of extreme violence [...]."42 Magnan's differentiation between alcoholism and absinthism was criticized at the time and has been more recently dismissed as insufficient.5

Wormwood's reputation was reinforced by exaggerated fictional accounts of absinthe's effects. Marie Corelli's widely-read 1890 novel Wormwood: A Drama of Paris, colorfully describes an absinthe experience: "I drank till the solid walls of my own room, when at last I found myself there, appeared to me like transparent glass shot through with emerald flame. Surrounded on all sides by phantoms,--beautiful, hideous, angelic, devilish [...]."43 Absinthe historian Phil Baker aptly describes Corelli's book as, "sublimely over-the-top",6 and it is generally accepted that her descriptions of absinthe intoxication are fanciful.

However, not all accounts of absinthe's hallucinogenic effects can be easily dismissed. Absinthe historian Jad Adams argues that black market absinthes containing high amounts of thujone may be capable of causing hallucinations.44 He finds support in Oscar Wilde's writings on absinthe, "The first stage is like ordinary drinking, the second when you begin to see monstrous and cruel things, but if you can persevere you will enter in upon a third stage where you will see things that you want to see, wonderful and curious things." This may be another example of artistic license, but Wilde, unlike Corelli, was an enthusiastic fan of the drink.

Despite a lack of solid evidence, some absinthe vendors claim, apparently as a marketing technique, that wormwood has psychedelic effects. One online vendor reports that "it is the 'thujone' in wormwood that gives absinthe its hallucinogenic properties."45 Another vendor claims: "The higher the Thujone level the stronger the psychedelic effect."46 These claims continue a tradition of promoting the drink's decadence and danger to lend it allure. As Phil Baker notes, "People want absinthe to be fearful stuff, with the distinctive form of pleasure that fearful things bring".1 In 1998, The Daily Mirror compared absinthe to vodka, cannabis, and LSD combined. A British importer, Tom Hodgkinson of Green Bohemia, is said to have responded, "You can't buy that kind of publicity".6 He elsewhere noted, "For me, one of the principle attractions of absinthe is that by drinking it, one is cocking a snook at New Labour's nanny culture."1

Other vendors and enthusiasts are equally intent on denying that wormwood has psychedelic effects. The Wormwood Society's website states "[Absinthe] won't make you 'trip', hallucinate, cut your ear off, or anything else you wouldn't ordinarily do when intoxicated with liquor."

Is Absinthe Uniquely Psychoactive?

There is currently little research on the effects of thujone in alcoholic beverages. As previously noted, there is some evidence that interactions between ethanol and α-thujone in absinthe may produce inebriation qualitatively different from the effects of ethanol alone. However, it is still a matter of debate whether a psychoactive dose of thujone is contained in most absinthes.

Dettling et al. performed a controlled study measuring the influence of α-thujone in alcohol on mood and attention in humans. Twenty-five subjects were administered either alcohol alone or alcohol with a 10 or 100 mg/L dose of α-thujone, yielding blood alcohol concentrations of about 0.05%. Subjects given the highest thujone dose demonstrated a small but detectable decrease in peripheral attention and experienced a decrease in the anxiety-reducing effect of alcohol, but no other effects were observed.14 To date, this is the most concrete supporting evidence for thujone's pyschoactivity.

Additionally, Matthew Baggott, researcher and author of The Absinthe FAQ,15 notes that animal experiments with thujone suggest that with recurring use, "Small ineffective doses may accumulate in the body to the point of having psychoactive and toxic effects. If this is the case, it validates absinthe's reputation for producing an unusual intoxication."15 Nonetheless, he concludes that this theory is speculative and observes that for now, "it seems reasonable to take reports of absinthe's uniqueness with skepticism."

Debate over Thujone Content

European Union regulations permit a maximum of 35 mg/L thujone in the strongest absinthe bitters,17 an amount that falls between the 10 mg/L that Dettling et al. found produced insignificant effects and the 100 mg/L that produced statistically significant effects. However, many modern commercial absinthes contain less than the EU maximum. In 2005, Lachenmeier et al. measured the thujone content in a number of modern commercial absinthes and reviewed three additional studies.12 Of the 147 bottles analyzed by various authors, 115 (78%) contained 10 mg/L thujone or less (as required by the EU for absinthe beverages containing 25% alcohol or more) and only 7 (5%) contained more than 35 mg/L.

Until recently it was believed that pre-ban or vintage absinthes contained significantly more thujone. In 1992, biochemist Wilfred Arnold published a widely-cited calculation that vintage absinthes contained around 260 mg/L.9 However, this number was based on overly high estimates of the thujone content of wormwood used in absinthe production and assumed that no thujone would be lost during post-maceration distillation. Absinthe enthusiast and vendor Ted Breaux of Viridian Spirits used gas chromatography to analyze vintage absinthes and modern absinthes made using traditional recipes. In media interviews, he reported finding very little thujone in the samples--many around 5 mg/L.3,47

Dale Pendell, author and herbalist, says that wormwood he has grown loses its potency quickly after being harvested. In an unpublished response to a New Yorker article about Breaux, Pendell quips, "If Mr. Breaux has no thujone in his distillate [absinthe], it is because he had no thujone in his pot [...] the wormwood must be fresh and of a good strain. Almost all of the commercially dried wormwood that I've tested were 'without virtue'."48 Lachenmeier agrees that age reduces thujone content, saying, "Based on anecdotal evidence from personal communications with absinthe distillers, there appears to be an inverse correlation between length of drying time of the wormwood and the amount of thujone in the final distillate."4

Breaux's widely-publicized findings were never published; however one peer-reviewed paper had similar findings. Lachenmeier et al. made three batches of absinthe according to select nineteenth-century recipes and analyzed the result with gas chromatography/mass spectroscopy. They found extremely low thujone concentrations, with maximum α- and β- thujone levels of 0.8 and 4.3 mg/L respectively. As previously noted, thujone levels in wormwood essential oils vary dramatically between different plants. Unfortunately, Lachenmeier et al. did not report the thujone content of the wormwood they used, and their ingredient plants likely contained low concentrations of thujone.

The authors also analyzed one old bottle of absinthe, a circa 1930 Pernod Tarragona produced in Spain after most of Europe banned absinthe. It contained 0.5 mg/L α-thujone and 1.3 mg/L β-thujone--far less than the 260 mg/L predicted by Arnold in 1992 and less than was found to produce statistically significant behavioral differences by Dettling et al. in 2004. The thujone content of the 1930 absinthe may have decreased over time. The authors attempted to assess the influence of aging on thujone and found that β-thujone degrades rapidly under exposure to UV light. While α-thujone appeared to be more stable, its behavior over the course of decades is unknown.

New yet-to-be-published research by Lachenmeier, Nathan-Maister, and Breaux reportedly examines more than ten vintage bottles of absinthe and finds substantially higher levels of thujone than previously reported by Breaux or Lachenmeier,49 but still far lower than Arnold's 260 mg/L. [Note: This article by Lachenmeier et al. was published a few months after this Extracts article and found a median concentration of 33 mg/L; see "Systematic Misinformation about Thujone in Pre-ban Absinthe".)

A separate lab also found very different results reproducing traditional recipes. In 2006, Gimpel et al. made absinthe with three Swiss recipes, documenting the thujone content of the Artemisia absinthium they used as well as of the finished products. They found that the thujone content of dried wormwood declines over time. They also showed a wide variation in the thujone content of plants tested--from "less than 0.1 to 4.8 mg per gram of dried herb".13 Using wormwood that had been dried less than four months, they produced absinthe containing between 61 and 101 mg/L thujone. Their absinthes, unlike those tested by Breaux and Lachenmeier, reached the level shown in the Dettling paper to be psychoactive.

In 2007, Lachenmeier and Nathan-Maister rejected Gimpel's higher thujone findings, arguing that they were based on non-traditional absinthe recipes. Their primary criticism was that Gimpel used Artemisia absinthium in the second maceration instead of A. pontica.

Lachenmeier and Nathan-Maister, who express a preference for less bitter, clear absinthes, consider high-thujone absinthes to be "unauthentic". However, a bias is revealed in their statement that one of the types of wormwood they used is "obviously thujone-free and, therefore, ideally suited to produce absinthe with wormwood quantities on the basis of the traditional recipes, without the producer facing the risk of exceeding the thujone limit." There is no indication that a traditional absinthe producer would have used contemporary thujone restrictions as a criteria in selecting wormwood.

Lachenmeier and Nathan-Maister provide an estimate of 0 to 76 mg/L of thujone in absinthe based on three factors: the thujone content of wormwood found in their literature review, their estimate of the percentage of thujone surviving the production process, and the varying amounts of wormwood used in the traditional absinthe recipes they selected. However, mean thujone content of wormwood samples from around the world may have little to do with the thujone content of wormwood used in vintage absinthes.

"[...] what [researchers] actually show is that the thujone content of absinthe depends greatly on the specific type of wormwood used."

The disagreement between Lachenmaier and Gimpel highlights a crucial variable in absinthe research. While Lachenmaier and Nathan-Maister set out to show that traditional absinthes have lower levels of thujone than previously thought, what they actually show is that the thujone content of absinthe depends greatly on the specific type of wormwood used. Low-thujone-content wormwood will result in low-thujonecontent absinthe. Over the last several hundred years a wide range of beverages have been called "absinthe", ranging from commercially-made alcohols sold by large distilleries to quasi-medicinal elixirs to homemade liquors. Some "absinthes" are little more than high-ethanol moonshine with wormwood and anise soaked in it for a few days or fortified with essential oil of wormwood. The results of absinthe analyses depend greatly on what recipe, thujone source, and production methods are chosen by the researchers.

The question of what constitutes an "authentic" absinthe is a matter of debate. Connoisseurs frequently argue about whether or not brightly-dyed Czech absinthes should be considered authentic, or whether an absinthe made using southern wormwood (A. abrotanum) is worthy of the name. Such debates become of scientific concern when they determine which absinthes should be included in analytical samples. Whether or not nineteenth-century absinthe contained much thujone is complicated by the fact that there are currently companies and individuals with financial interest in finding that "authentic" absinthe is low in thujone.

Many basic questions regarding wormwood and its role in our culture have yet to be decisively answered. Clear answers can only come from further research--particularly experimental investigations of the psychopharmacology of thujone in humans.